Heartbeat is controlled by a dual pathway: the parasympathetic nervous system (which slows the heart down, allowing it to rest) and the sympathetic nervous system (which speeds it up, increasing its activity). Some medications, such as bisoprolol, inhibit the sympathetic nervous system, slowing the heart rate and thus lowering blood pressure. Heart rate (HRV) reflects the strength of the parasympathetic nervous system. High HRV indicates a voluntary and relaxed heartbeat, while low HRV indicates a constant heart rate and fatigue. Magnesium activates the parasympathetic nervous system, while alcohol activates the sympathetic nervous system. Drinking alcohol causes a sharp drop in HRV. 😂